XVI INTRODUCTION. 



greenish tinge, due perhaps to the combined influence of the somewhat 

 ochreous coloration combined with these black scales. The green 

 colour, therefore, is not essentially a pigment colour at all. It is, in 

 fact, almost identical with the gloss on our dark Pararge cegeria and in 

 both cases entirely independent of the pigment colour beneath it. The 

 darkening is apparently brought about by a similar action to that 

 occurring in the dark F. urticcv before referred to. There appears to 

 be no doubt about the origin of the green on the undersides of some of 

 the Argynnids. In A. aglaia, a long series of undersides gives every 

 transition between yellow, green and bright fulvous-red, whilst the 

 green in the undersides of Argynnis paphia shades off occasionally into 

 the most exquisite pink reflections, and showing an undoubted tendency 

 to produce highly developed unpigmented scale structure. But so far 

 I am very much in doubt about the pigmented character of the green 

 found in the undersides of these species, and although its transitions 

 point it out as such, yet it is not at all safe to assume that it is so. 



It is strange that the greens of the undersides of these Argynmdce, 

 of Theda rubi, and of the uppersides of the various species of Proem, are 

 so readily convertible into brown, and yet we have to look upon them 

 in the light of our present knowledge as probably possessing but little 

 pigment. The mere closure of these species in a damp box changes 

 their coloration to a bronzy or red-brown, the original colour being 

 restored by exposure to the air. If these colours are in any way pig- 

 mental, the change is quite regular genetically, but if not, we must 

 suppose that the presence of the vapour which is deposited on the 

 scales, alters the effect produced when the light falls upon them. 

 However, it is at present rather difficult to deal with these colours. 



It is easy to speak much more certainly of the beautiful green in the 

 fore wings of Callimorpha dominula. In this species the green, I 

 believe, is certainly unpigmented, and it seems impossible to bleach it 

 or alter it permanently in any way. It remains under almost all ex- 

 periments unchangeable. But a clue to the development of this 

 beautiful green is found in its ally C. hera. This species has the dark 

 markings of the fore wings brown, with here and there a superficial 

 metallic gloss. This brown pigment is not at all difficult to remove, 

 and as the pigment gradually disappears, the metallic gloss shows up 

 as a brilliant surface green of the same character as that in C. dominula, 

 but of course less strongly developed. The green in these species 

 appears to be unpigmented beyond doubt. 



I was always under the impression that the yellow and green 

 metallic markings found in the genus Plusia &c., were unpigmented, 

 and was rather startled to find that the pigments were removable, and 

 that the metallic appearance was purely superficial and due to a sur- 

 face gloss which was entirety independent of the pigment underlying 

 it. Thus I have a Plusia chrysitis in which the colour is practically 

 obsolete, but the metallic appearance remains, the ghost of its original 

 self. The pigmented character of these metallic markings was one of 

 the most surprising and interesting facts I have met with in studying 

 the relationship of colour in insects. After I had discovered it, the 

 surprise appeared rather in not having surmised it before, since I knew 

 that the less perfectly developed gloss in such species as Hydrcecia 

 micacea, H. nictitans, the undersides of Xylophasia sublustris &c., of 

 Pararge aigcria and Satyr us acntde was perfectly independent uf the 

 pigment in these species. 



